This invention relates to vehicle tire parameter monitoring systems. More particularly, this invention relates to a fire parameter monitoring system having a sensor unit position location feature using permanent magnets.
Tire parameter monitoring systems are known and are commonly used to monitor one or more parameters of interest in individual pneumatic tires of a vehicle and to provide an advisory signal to the driver, usually via an on-board computer system, containing information about the fire parameter(s). The portion of the fire parameter monitoring system located at or in the individual fires is termed the sensor unit, and is coupled to one or more sensors capable of measuring the parameter(s) of interest and generating an electrical signal representative of the value of the measurement, a signal generator (typically an r.f. signal generator) capable of generating a wireless signal corresponding to the electrical signal, a microcontroller (such as a microprocessor or a digital signal processor) and a power source. Electrical power to the sensor circuitry is usually provided by a battery, which must be replaced (if possible) when the available battery power drops below a useful level. In some known systems, the battery cannot be replaced so that the entire sensor assembly must be replaced when the battery has reached the end of its useful lifetime. A tire parameter sensor system which monitors internal tire pressure is disclosed in commonly assigned, U.S. Pat. No. 6,959,594 issued Nov. 1, 2005 for “External Mount Tire Pressure Sensor System”, the disclosure of which is hereby incorporated by reference. A tire pressure monitoring system which incorporates a power saving unit providing extended useful battery life is disclosed in commonly assigned, U.S. Pat. No. 7,222,523 issued May 29, 2007 for “Tire Pressure Sensor System With Improved Sensitivity And Power Saving”, the disclosure of which is hereby incorporated by reference. A tire parameter monitoring system which eliminates the usual battery is disclosed in commonly-assigned, co-pending patent application Ser. No. 11/473,278 filed Jun. 22, 2006 for “Tire Parameter Monitoring System With Inductive Power Source” (the '278 application), the disclosure of which is hereby incorporated by reference.
The advisory signal produced by the sensor unit may indicate (a) whether a given parameter in the associated vehicle tire has a current value lying within or outside of a predetermined safe range, (b) the measured value of the parameter, or (c) some other fire parameter information of interest. Examples of common tire parameters are internal tire pressure, tire temperature, internal tire air temperature, and lateral tire force. In some cases, the parameter may be related to the condition of the wheel on which the tire is mounted, such as the angular moment of the wheel, concentricity or the like.
The advisory signal is typically generated by the r.f. signal generator controlled by the microprocessor connected to the tire parameter sensor, the advisory signal being generated in accordance with the system design characteristics: i.e., whether the system uses the range indicator value (in range/outside range), the measured value, or the other information of interest. This r.f. signal is transmitted to a vehicle-mounted receiver, which uses the advisory signal to alert the driver either visually (by activating a warning lamp or display) or audibly (by activating an audible alarm) or both. Alternatively, or in addition, the receiver may use the advisory signal for some other system purpose, such as to activate a vehicle control system, such as braking control, suspension control, and the like; to store the parameter data for future analysis; or for any other desired purpose.
In order to provide an operable system, it is necessary to correlate the advisory signals received by the vehicle-mounted receiver with the physical location on the vehicle of the tire whose parameter condition is specified by a given advisory signal. In the past, various techniques have been devised for this purpose. A common technique is the inclusion of an identification signal along with the parameter condition in a given advisory signal: the identification signal is unique to the sensor unit which generates the parameter condition. This unique identification signal is initially correlated to tire location on the vehicle by a technician having the required skill and training to operate the system in an initial training mode. Once each sensor unit has been initially correlated to its physical location on the vehicle, any advisory signal generated by a given sensor unit and received by the vehicle-mounted receiver can be uniquely identified with the location of the tire whose parameter condition is specified by the advisory signal.
A disadvantage with this type of location correlation technique is that any change to the original tire and sensor unit location requires that the system be re-correlated. For example, if the vehicle tires are relocated to different positions in the normal course of vehicle servicing, the physical locations of the sensor units will change if the sensor units are fixed to the tires or the wheels on which the tires are mounted (which is typical), and each individual sensor unit must be re-correlated to the physical location of the associated tire. The same is true (a) when a spare tire is exchanged for a flat tire on the vehicle; (b) when one or more new tires are installed on the vehicle wheels and mounted on the vehicle; and (c) when a new sensor unit is installed in place of a unit which stops functioning property. As noted above, re-correlation requires the efforts of someone having the required skill and training to operate the system in a training mode. While some vehicle owners may be capable of acquiring the necessary skill and training, others may not. The latter will necessarily suffer delay and expense when re-configuring the vehicle tires and wheels; the former will suffer at least the delay attendant upon re-familiarizing oneself with the steps required to re-program an electronic system.
A variation of this type of sensor unit correlation system uses a manually actuatable transmitter installed in the valve stem of a tire. The transmitter is actuated by inserting a small object into the valve stem a sufficient axial distance to operate a switch, which causes the transmitter to send an appropriate signal to a vehicle-mounted receiver capable of correlating the signal from the operating transmitter to the tire to which the transmitter is attached. An example of this type of system is disclosed in U.S. Pat. No. 6,998,975 B2 issued Feb. 14, 2006, the disclosure of which is hereby incorporated by reference. This system requires some provision for ensuring that any change to the original sensor unit/tire location configuration will cause a re-correlation of the sensor units with the new configuration.
Another common technique used to correlate the advisory signals received by the vehicle-mounted receiver with the physical location on the vehicle of the tire whose parameter condition is specified by a given advisory signal incorporates a special multiple antenna interrogator system connected to a vehicle-mounted controller and a complementary set of sensor units. Each antenna is connected to the controller in such a way that only one antenna is actively coupled to the controller during any given interrogation interval. Each antenna is located adjacent a different associated one of the sensor units in sufficiently close proximity that an interrogation signal generated by a given antenna is operatively coupled essentially only to the associated sensor unit. Each sensor unit has a circuit responsive to an interrogation signal from the associated antenna to initiate a parameter signal transmission sequence during which the value measured by a sensor is transmitted to a receiver located in the vehicle-mounted controller, where it is processed. Since the location of each individual interrogation antenna is fixed, it can be permanently correlated to a wheel location. Therefore, when the controller activates a given interrogation antenna, the subsequently received parameter signal is automatically correlated with the correct tire location. Examples of this type of unit are disclosed in U.S. Patent Application Publication No. US 2003/0145650 A1 published Aug. 7, 2003; and U.S. Pat. No. 6,838,985 B2, the disclosures of which are hereby incorporated by reference.
A disadvantage to the interrogator antenna system described above lies in the requirement for the installation of the separate interrogation antennae adjacent the tire parameter sensor units. The necessary electrical cabling must be routed between the controller and the individual antennae. This imposes a requirement of careful routing of the cables to avoid mechanical abrasion, electrical interference, and thermal stresses over time. As a consequence, installation cost and hardware durability are factors of concern when deciding to implement such a system.
Efforts to provide a simple, inexpensive, reliable, and accurate sensor unit location feature for a tire parameter sensing system devoid of the above-noted disadvantages have not been successful to date.